Battery and inverted flight?

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francesco.doenz
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Battery and inverted flight?

Post francesco.doenz »

Why does the battery have to be isolated from the electrical system during inverted flight?
Many thanks for your inputs!
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TheAerialAssassin
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Re: Battery and inverted flight?

Post TheAerialAssassin »

Electrolyte splashing around in the battery and not covering the plates? Just a guess.

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AKar
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Re: Battery and inverted flight?

Post AKar »

A very good question I should know the answer but I readily don't.

My best intuitive guess would come up from their natural properties. The lead-acid batteries tend to pile up some stuff, composition of which depends on the exact chemistry of the battery, on the bottom of the cell bowls. The plates in the battery are dimensioned so that they won't come too close of the bottom of the battery, because of the residue accumulation. Some designed for deeper discharge, such as truck batteries, have a larger clearance. This is a natural propery of a lead-acid battery, and some of such designed for a continuous, deep discharge actually have larger physical margins until the plates are contacted. In any case, the material has a capability to short a cell or more, resulting in an inter-battery short-circuit, should the external connection provide a common potential. If you flip the battery around, the stuff will float in between the plates up to the up-end, potentially giving you an issue. You'd want to have the battery to be disconnected from the system should it short internally.

Anyways, a good question - I need to study this one out. :)

-Esa
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francesco.doenz
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Re: Battery and inverted flight?

Post francesco.doenz »

But it's the first time I read this....? I own also P47, Spit and P51...?
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AKar
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Re: Battery and inverted flight?

Post AKar »

Well, someone has made the system to take it up for you. :) It may have not been a worth of a mention in the later planes, or the exact battery chemistry may be a bit different. There is quite a bit going on in the background regardless.

-Esa
Let me imagine what is impossible - and then do it.

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Killratio
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Re: Battery and inverted flight?

Post Killratio »

I don't know Francesco.

But in the Spitfire, of course, the Accumulator can NOT be isolated without turning everything off individually.

Interesting! A different chemical makeup or design in the T-6 battery would be my best guess.
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Great Ozzie
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Re: Battery and inverted flight?

Post Great Ozzie »

AKar wrote:A very good question I should know the answer but I readily don't.
Your guess sounds about right Esa.

There's a good pdf out there entitled: The Automotive Storage Battery Its Care and Repair by Otto A. Witte (There's a Kindle version too fwiw). It actually refers to the "residue" as "sediment" or "lead mud". A lot of interesting stuff in it (a lot of great pictures too).
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AKar
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Re: Battery and inverted flight?

Post AKar »

Apparently, as it turns out after a brief research, this feature in T-6 is in place to protect the battery "from excessive gas pressure preventing the battery vents from opening when the airplane regains its normal flight position", as the maintenance manual has it. Quite an interesting feature, to me it sounds that the battery is basically a regularly vented one, but some kind of flapper vents prevent the loss of electrolyte when inverted. But of course if there are such, any excessive internal pressure would prevent them from opening again. To avoid build-up of that pressure, the battery circuit is opened when the airplane is inverted and the vents closed.

I wonder how the batteries in other warbirds of time were protected from this issue. Nowadays, of course, a completely sealed, likely an AGM-type battery would be used in an aerobatic airplane, and no need for this mercury switch remains.

Interesting book by Witte! Lots in it is of course still applicable today, and it has quite a nice historical perspective into the topic. Thanks for the tip! :)

-Esa
Let me imagine what is impossible - and then do it.

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